A piezoelectric element usually comprises lower and upper electrodes, and ferroelectric or paraelectric crystallized piezoelectric ceramic held between these electrodes. As to the piezoelectric ceramic, lead zirconate titanate (hereinafter referred to as “PZT”), or “PLZT type” in which lanthanum is added to PZT is general. For example, a ferroelectric article using PZT has been described in Applied Physics Letters 1991, vol. 58, No. 11, pp. 1161 to 1163.
There is an ink jet system recording head as an application example of a piezoelectric element using a thin-film piezoelectric ceramic. A film thickness of about 1 μm to 25 μm is necessary for the piezoelectric thin film for use in this application to develop an electromechanical conversion function (pressure which promotes displacement). Uniformity of the film has been demanded in order to control the displacement with good precision.
Examples of a process of manufacturing a metal oxide type piezoelectric thin film include a sputtering process, a metalorganic chemical vapor deposition process (MOCVD process), a sol-gel process and the like. In the sol-gel process, a solution or a dispersion solution containing a hydrolytic compound of each component metal constituting a raw material, a partial hydrolytic material, or a partial polycondensation material is applied to a substrate. After the coated film is dried, the film is heated in air to form a film of metal oxide. Furthermore, the film is fired at a temperature which is not less than the crystallization temperature of metal oxide to thereby form the piezoelectric thin film.
As the hydrolytic metal compound which is a raw material, metal alkoxide, or an organic metal compound such as a partial hydrolysis material or partial polycondensation material has been generally used. In the sol-gel process, the piezoelectric thin film can be formed most inexpensively and easily.
As a method which is similar to the sol-gel process, there is a metalorganic decomposition process (MOD process). In the MOD process, a pyrolytic metalorganic compound (metal complex and metalorganic acid salt), for example, a solution containing a metal β-diketone complex or carboxylate is applied to a substrate. The solution is heated, for example, in air or oxygen, evaporation of a solvent in a coating film, and pyrolysis of a metal organic compound are caused to thereby form a film of metal oxide. Furthermore, the film is fired at a temperature which is not less than the crystallization temperature, and the film is crystallized. In the present invention, the sol-gel process, MOD process, and a mixed process are referred to as the “sol-gel process”.
Moreover, an ink jet system printer head using a piezoelectric element formed into a film by the sol-gel process has been described. For example, in Japanese Patent Application Laid-Open No. H9-92897, Japanese Patent Application Laid-Open No. H10-139594, and Japanese Patent Application Laid-Open No. H10-290035, a method has been described in which the sol-gel process is utilized, sol containing a piezoelectric material is applied to a lower electrode a plurality of times, a heating process is repeated, and accordingly the piezoelectric thin film of the piezoelectric element for use in an ink jet system printer head is formed.
However, a crystal system or orientation has differed, or a composition ratio of a metal compound has fluctuated depending on a portion in a piezoelectric film such as a PZT film formed by the sol-gel process until now. Therefore, it cannot be easily said that an electric or piezoelectric performance of the piezoelectric film can be controlled to be optimum.